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Issue 6, 2013
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Amide I vibrational mode suppression in surface (SERS) and tip (TERS) enhanced Raman spectra of protein specimens

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Abstract

Surface- and tip-enhanced Raman spectroscopy (SERS and TERS) are modern spectroscopic techniques, which are becoming widely used and show a great potential for the structural characterisation of biological systems. Strong enhancement of the Raman signal through localised surface plasmon resonance enables chemical detection at the single-molecule scale. Enhanced Raman spectra collected from biological specimens, such as peptides, proteins or microorganisms, were often observed to lack the amide I band, which is commonly used as a marker for the interpretation of the secondary protein structure. The cause of this phenomenon was unclear for many decades. In this work, we investigated this phenomenon for native insulin and insulin fibrils using both TERS and SERS and compared these spectra to the spectra of well-defined homo peptides. The results indicate that the appearance of the amide I Raman band does not correlate with the protein aggregation state, but is instead determined by the size of the amino acid side chain. For short model peptides, the absence of the amide I band in TERS and SERS spectra correlates with the presence of a bulky side chain. Homo-glycine and -alanine, which are peptides with small side chain groups (H and CH3, respectively), exhibited an intense amide I band in almost 100% of the acquired spectra. Peptides with bulky side chains, such as tyrosine and tryptophan, exhibited the amide I band in 70% and 31% of the acquired spectra, respectively.

Graphical abstract: Amide I vibrational mode suppression in surface (SERS) and tip (TERS) enhanced Raman spectra of protein specimens

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Article information


Submitted
01 Aug 2012
Accepted
03 Jan 2013
First published
07 Jan 2013

Analyst, 2013,138, 1665-1673
Article type
Paper

Amide I vibrational mode suppression in surface (SERS) and tip (TERS) enhanced Raman spectra of protein specimens

D. Kurouski, T. Postiglione, T. Deckert-Gaudig, V. Deckert and I. K. Lednev, Analyst, 2013, 138, 1665
DOI: 10.1039/C2AN36478F

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